Guitar Chord Theory: How Every Chord Is Built (Beginner-Friendly)

Most guitarists learn chords by shape—copy a diagram, move your fingers, done. That works for a while. But when you understand how chords are actually built, everything clicks: why certain chords go together, what "add9" means, why a G7 wants to resolve to C, how to build any chord anywhere on the fretboard.

Chord theory isn't complicated. You just need a few building blocks, and this guide walks you through all of them—from basic triads to extended chords—with guitar-focused examples throughout.

The Foundation: Intervals

Before chords, you need to understand intervals—the distance between two notes. On guitar, intervals are measured in semitones (frets). Moving one fret = one semitone.

The most important intervals for building chords are the 3rd and the 5th. Together with the root, they form a triad—the basic building block of all chords.

Triads: The Foundation of All Chords

A triad is a three-note chord built from stacked thirds. There are four types:

Major Triad — Formula: 1 – 3 – 5

Built with a root, major 3rd (4 semitones), and perfect 5th (7 semitones). Sound: bright, happy, stable.

C Major = C – E – G
G Major = G – B – D
D Major = D – F# – A

Minor Triad — Formula: 1 – ♭3 – 5

Same as major, but the 3rd is lowered by one semitone (minor 3rd = 3 semitones). Sound: dark, sad, emotional.

C Minor = C – Eb – G
A Minor = A – C – E
E Minor = E – G – B

Diminished Triad — Formula: 1 – ♭3 – ♭5

Both the 3rd and 5th are lowered. Sound: tense, unstable, unsettling.

B Diminished = B – D – F
C Diminished = C – Eb – Gb

Augmented Triad — Formula: 1 – 3 – #5

Major 3rd, but the 5th is raised one semitone. Sound: mysterious, tense, dreamlike.

C Augmented = C – E – G#
G Augmented = G – B – D#

The Critical Difference: Major vs Minor

The distinction between major and minor comes entirely from one note—the 3rd. Compare:

A Major = A – C# – E   (major 3rd: C#)
A Minor = A – C  – E   (minor 3rd: C)

The only difference: C# vs C

This is why the same chord shape moved up or down a fret can dramatically change the sound. The 3rd is the emotional "colour" of the chord.

Power Chords: 1 – 5 (No 3rd)

Power chords omit the 3rd entirely, containing only the root and perfect 5th. This makes them neither major nor minor—they sound powerful and work over any scale.

E5 = E – B   (open E string + 2nd fret A string)
A5 = A – E   (open A string + 2nd fret D string)

Power chords cut through distortion cleanly, which is why they dominate rock and metal. Learn more in our power chords guide.

Suspended Chords: Replacing the 3rd

Instead of removing the 3rd, suspended chords replace it with a 2nd or 4th—creating tension that "wants to resolve."

Sus2 — Formula: 1 – 2 – 5

Dsus2 = D – E – A
e|--0--|
B|--3--|
G|--2--|
D|--0--|
A|-----|
E|-----|

Sus4 — Formula: 1 – 4 – 5

Dsus4 = D – G – A
e|--3--|
B|--3--|
G|--2--|
D|--0--|
A|-----|
E|-----|

Sus chords are common in pop songwriting. A classic move: Dsus4 → D, which sounds like a chord "arriving home."

Adding the 7th: Beyond Basic Triads

Add a 7th above the triad and you open up a whole new world of color. There are four main types of 7th chords:

The Dominant 7th: Most Important Chord in Harmony

The dominant 7th chord (e.g. G7) creates the strongest pull in Western music. It contains a tritone (the most dissonant interval) between its 3rd and 7th, which desperately wants to resolve.

G7 = G – B – D – F
     ↑           ↑
     3rd (B) and ♭7th (F) = tritone tension

This V7→I resolution is the engine behind blues, jazz, classical cadences, and most Western pop.

Extended Chords: 9ths, 11ths, 13ths

Extensions continue stacking thirds above the 7th. On guitar, you often omit certain notes (usually the 5th) to keep the shape playable.

9th Chords — Adding the 9th (= 2nd, one octave up)

Cmaj9  = C – E – G – B – D   (1–3–5–7–9)
C9     = C – E – G – Bb – D  (dominant 9th)
Cm9    = C – Eb – G – Bb – D (minor 9th)

Add Chords — Extension Without the 7th

"Add" means add the note without including all the 7th chord layers. Common in pop:

Cadd9  = C – E – G – D   (no 7th — brighter than C9)
Gadd9  = G – B – D – A   (very common in pop)

Diatonic Chords: How Chords Fit Into Keys

Every major key has 7 diatonic chords—one built on each scale degree. These chords all share the same notes as the scale, so they naturally sound good together.

The pattern is always the same regardless of key:

Scale Degree:  I      ii     iii    IV     V      vi     vii°
Chord Type:    Major  minor  minor  Major  Major  minor  dim

Key of C:      C      Dm     Em     F      G      Am     Bdim
Key of G:      G      Am     Bm     C      D      Em     F#dim
Key of D:      D      Em     F#m    G      A      Bm     C#dim

The Roman numeral system tells you the function of each chord. I, IV, and V are major. ii, iii, and vi are minor. vii° is diminished.

Secondary Dominants: Borrowing Tension

You can create a dominant 7th chord targeting any chord in the key, not just the I chord. This is called a secondary dominant.

In C major:
V7/V  = D7  (dominant of G — adds tension before G)
V7/ii = A7  (dominant of Dm — pulls strongly to Dm)
V7/vi = E7  (dominant of Am — common in pop/jazz)

Chord Inversions

A chord doesn't have to have its root as the lowest note. Changing the bass note creates an inversion:

C Major (root position): C – E – G  (C is bass)
C/E (1st inversion):     E – G – C  (E is bass)
C/G (2nd inversion):     G – C – E  (G is bass)

Written as "slash chords": C/E, C/G

Inversions create smooth bass lines and voice leading. The classic descending bass line uses inversions:

C – C/B – Am – Am/G – F – G – C
(bass: C – B – A – G – F – G – C)

Quick Reference: Chord Formulas

Putting It Into Practice

Here's how to apply chord theory to your playing right now:

1. Pick any chord you know — find its root, 3rd, and 5th on the fretboard
2. Lower the 3rd one fret — hear how it shifts from major to minor
3. Add the 7th — on the next string, find the note 10 or 11 semitones from the root
4. Build your own chord — find any root, stack the intervals above it
5. Analyze songs you love — identify the chord type and why it sounds the way it does

The fretboard becomes a much more logical place once you see chords as interval patterns rather than memorized shapes. The same formula works in every key, every position.

Next Steps

Now that you understand how chords are built, explore:

• Guitar Chord Progressions for Beginners — Use your chord knowledge to build great-sounding progressions
• Guitar Keys Explained — Understand how chords relate to each other in a key
• Barre Chords for Beginners — Apply chord theory to moveable shapes across the fretboard
• Guitar Scales for Beginners — Learn the scales that chords are constructed from